dt-bindings: crypto: ice: Document sc7280 inline crypto engine

Document the compatible used for the inline crypto engine found on
SC7280.

Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>